优化问题列表组件，调整默认题目和答案值，增强用户体验

ui/src/components/study/ProblemList.vue

@@ -1,6 +1,6 @@
 <template>
   <v-data-table :loading="loading" :headers="(headers as any)" :items="problems"
-    :sort-by="[{ key: 'id', order: 'asc' }, { key: 'problem', order: 'asc' }]" multi-sort>
+    :sort-by="[{ key: 'id', order: 'asc' }, { key: 'problem', order: 'asc' }]" multi-sort items-per-page-text="每页">
     <template v-slot:loading>
       <v-skeleton-loader></v-skeleton-loader>
     </template>
@@ -170,8 +170,8 @@ const editedItem = ref({
 });
 const defaultItem = ref({
   id: 0,
-  problem: '1',
-  answer: '1',
+  problem: '',
+  answer: '',
   check_error: 0,
 });